Human infection with the H7N9 virus is a relatively new and emerging respiratory illness that was first identified in China in 2013. It is a subtype of avian influenza A virus and primarily affects poultry, but can also infect humans. Understanding the epidemiology of H7N9 virus is crucial to prevent and control its spread.
Global Prevalence: Since its discovery in 2013, H7N9 virus has predominantly been reported in China. The majority of cases have occurred in eastern China, particularly in the provinces of Zhejiang, Guangdong, Jiangsu, and Shanghai. However, sporadic cases or small outbreaks have also been reported in other countries, including Hong Kong, Taiwan, Malaysia, and Canada, although these cases were mostly linked to travel from affected areas in China.
Transmission Routes: The primary mode of transmission of the H7N9 virus is through contact with infected poultry or their environments, such as live poultry markets. Direct contact with infected birds, their secretions (such as saliva, nasal discharge, and feces), or contaminated surfaces can lead to human infection. Limited human-to-human transmission has been reported, but it is not believed to be sustained or efficient.
Affected Populations: H7N9 virus infection predominantly affects individuals who have close contact with live poultry, such as poultry farmers, market workers, and consumers. It also disproportionately affects older adults, particularly those with underlying medical conditions. Children and younger adults have also been infected, but to a lesser extent.
Key Statistics: Since its emergence in 2013, there have been multiple waves of H7N9 virus infections in China. As of September 2021, a total of 1,568 laboratory-confirmed cases and 615 deaths have been reported. The case fatality rate is approximately 40%, indicating the severity of the disease. The number of cases has significantly decreased since 2017 due to various control measures implemented by the Chinese government, including poultry market closures and enhanced surveillance.
Historical Context and Discovery: H7N9 virus was first identified in China in March 2013 when several cases of severe respiratory illness with an unknown cause were reported. Initial investigations revealed a novel avian influenza A virus with a combination of genetic material from bird flu viruses found in ducks and chickens. It was subsequently named H7N9. The virus was traced back to live poultry markets, where infected birds were commonly found.
Major Risk Factors for Transmission: The major risk factors associated with H7N9 virus transmission include direct or close contact with infected poultry or their environments, such as visiting live poultry markets or handling sick birds. Occupational exposure, such as working in the poultry industry, also poses a significant risk. Additionally, individuals with weakened immune systems or underlying medical conditions are more susceptible to severe illness if infected.
Impact on Different Regions and Populations: The impact of H7N9 virus has been primarily concentrated in China, with sporadic cases reported in other countries. Within China, the prevalence rates and affected demographics have varied across different regions and over time. The eastern provinces of Zhejiang, Guangdong, Jiangsu, and Shanghai have consistently reported the highest number of cases. Older adults and individuals with underlying health conditions have been more severely affected by the virus.
In conclusion, the epidemiology of H7N9 virus highlights its primarily avian origin and its ability to infect humans. The virus is predominantly transmitted through contact with infected poultry and their environments, and human-to-human transmission is limited. The impact of H7N9 virus has been most significant in China, with variations in prevalence rates and affected demographics across different regions. Effective surveillance, control measures, and public health interventions are crucial to prevent and manage the spread of this emerging respiratory illness.

Download Data(下载数据)

Seasonal Patterns: The data shows that the number of H7N9 virus cases in mainland China has a distinct seasonal pattern. The cases generally increase during the winter months and reach a peak in January or February of each year. After the peak, the number of cases decreases steadily during the spring months before reaching a trough in the summer. The trend then remains relatively low until the next winter season.
Peak and Trough Periods: The peak period for H7N9 virus cases occurs in January or February of each year, with the highest number of cases reported during these months. The trough period, on the other hand, occurs during the summer months, particularly in July and August, when the number of cases is at its lowest.
Overall Trends: Looking at the overall trend, it can be observed that the number of H7N9 virus cases in mainland China has been relatively low since 2018. After reaching its peak in 2017, the number of cases has been decreasing gradually, with sporadic cases reported in the subsequent years. The data from 2020 onwards shows a significant drop in cases, with no reported cases since then.
Discussion: The seasonal patterns and overall trends of the H7N9 virus cases in mainland China indicate that there have been successful efforts in controlling and preventing the spread of the virus. The peak and trough periods align with the typical influenza season, which suggests that the virus may exhibit similar patterns to other seasonal influenza strains. The declining number of cases after 2017 suggests that public health measures and interventions have had a positive impact on reducing transmission. However, continued surveillance and vigilance are still necessary to ensure that the virus does not resurge.